The secret is to have the Acccessory Library loaded. If you go to Help>ArchiCAD 10 Goodies,
you
will be taken to
http://www.graphisoft.com/support/archicad/downloads/goodies10/USA.html
At the bottom of that page is the Accessories Library. You need to download it and load the extracted library with your project in order to use any of the Accessories.
On the website it says:
The Accessories Library is required for using the Accessories and Interior Wizard goodies. After downloading the file uncompress it into the ‘ArchiCAD 10/ ArchiCAD Library 10’ folder
.
If you put it in there, it will load automatically with your AC10 Library, but if you uninstall/reinstall AC10, it will probably be deleted! It was so much easier when this was bundled with the AC Library wasn't it?
Cheers,
Link.